Borehole logging tool with anchoring mechanism

ABSTRACT

A borehole tool, such as a seismic shuttle-type logging tool, including a tool body having at least one sensor package and an anchoring mechanism, the anchoring mechanism having a drive mechanism including a motor, a drive shaft and a clutch; an anchoring arm moveable between first (extended)and second (retracted) positions relative to the tool body; a push rod connecting the anchoring arm to the drive mechanism; and a spring acting to bias the arm into a first position relative to the tool body. The push rod extends through the clutch mechanism and is engaged by the spring to bias the arm into the first position, and is also driven by the drive mechanism through the clutch to move the arm between the first and second positions. The spring is a coil spring surrounding the drive mechanism and acting on the push rod directly.

TECHNICAL FIELD

The present invention relates to borehole logging tools, and inparticular to aspects of an actuating mechanism for a seismic shuttlelogging tool in which a sensor package is urged against the wall of aborehole.

BACKGROUND ART

Seismic shuttle logging tools are know for use in performing verticalseismic profile surveys from boreholes to evaluate the surroundingunderground formations. A multi-shuttle seismic tool comprises a numberof similar tools (shuttles) linked together by means of a cable andlogged through a borehole while seismic signals are generated at thesurface. At each measurement level, each shuttle is anchored to the wallof a borehole during a measurement operation by means of an anchoringarm. In VSP surveys, it is necessary to make measurements at a number oflevels in a borehole so the tool anchoring must be released to allow thetool to be moved and then re-engaged at the next level. The time takenfor the anchor to release and to re-engage can be a significant factorin the time taken to make a measurement at each level. In Schlumberger'sCombinable Seismic Imager tool (CSI) the anchoring arm of each shuttleextended under spring bias and a drive motor is used to provide theanchoring force or retraction. Aspects of the CSI are described in U.S.Pat. No. 4,563,757; U.S. Pat. No. 4,575,831; U.S. Pat. No. 4,987,969;and U.S. Pat. No. 5,200,581. In particular, patents '757 and '831 relatein particular to the anchoring mechanism and procedure. A schematicfigure from the patents is shown in FIG. 1. This prior art arrangementincludes a motor 35, an output reducer 36 with an electromagnetic brake37 and an output shaft to a coupling device 39 comprising a clutch 50, amechanical logic 51 and torque limiter 54. The mechanical logic 51includes studs located in helical, V-shaped, cam slots which serve tobring the clutch into engagement on operation of the motor. Drive istransmitted to a push rod 34 connected to the anchoring arms 31, 32 bymeans of a ball screw 40 and nut 41. The anchoring arms are urged awayfrom the tool body 29 by a leaf spring 43 which is fixed to the toolbody 29 and bears upon the arm 31. When in the open position, a pad 30at the end of the arms 31, 32 engages the borehole wall and causes thetool body 29 to be pushed against the opposite side of the boreholewhere it can be anchored for use. The motor 35 is used to provide theextra anchoring force to the arms 31,32 and to withdraw the arms whenthe tool is run in or pulled out of the borehole. When the tool is to bemoved to a different level, the action of the clutch 50 allows the motorto be disengaged and the arms held only by the force of the leaf spring43.

The present invention has as its object a tool which has an anchoringarm which can be anchored and released in a relatively short time and inwhich the anchoring mechanism can be relatively compact.

DISCLOSURE OF INVENTION

The present invention provides a borehole tool comprising a tool bodyhaving at least one sensor package and an anchoring mechanism, theanchoring mechanism comprising:

a) a drive mechanism including a motor, a drive shaft and a clutch;

b) an anchoring arm moveable between first and second positions relativeto the tool body;

c) a push rod connecting the anchoring arm to the drive mechanism; and

d) a spring acting to bias the arm into a first position relative to thetool body;

characterised in that the push rod extends through the clutch mechanismand is engaged by the spring to bias the arm into the first position,and is also driven by the drive mechanism through the clutch to move thearm between the first and second positions.

The invention is particularly applicable to shuttle-type seismicborehole logging tools although may also be applicable to any other typeof borehole tool which requires the tool body to be urged against theborehole wall. The provision of the push rod extending through theclutch mechanism allows the overall length of the anchoring mechanism tobe reduced over that provided by the prior art device. The sensorpackage can be a separate package with one or more sensors mounted onthe tool body or one or more sensors and associated electronics mountedin the tool body.

It is particularly preferred that a ball-bearing clutch is used whichcomprises a collar having a number of balls which engage in grooves inthe push rod to allow the drive mechanism to move the arm. A springloaded retaining ring can be provided to hold the balls in a drivingposition in the grooves when engaged by the collar.

The drive shaft is typically a drive screw and a nut is used to transmitthe driving force to the push rod. Driving force can be applied eitherthrough the clutch or by bearing surfaces on the nut which engagedirectly extensions of the push rod. The two mechanisms can be used toprovide reversible drive to the push rod.

The spring can be a coil spring which is located in the tool body aroundthe drive mechanism. Other arrangements of springs or resilient biasingmeans can be used to urge the arm into the first position.

The arm can be mounted on a pivot on the tool body with the firstposition being extending away from the tool body and the second positionbeing along the tool body. Thus, the spring can be used to urge the armaway from the tool body and the motor used to provide further drive inthis direction for anchoring force, or to provide a counteracting driveto withdraw the arm to the tool body. By reversing the drive to releasethe clutch, the arm can be held under spring force alone while the toolis moved in the borehole.

An arm position sensor can be used to indicate the exact position of thearm after movement.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic view of a prior art tool;

FIG. 2 shows a schematic view of a shuttle seismic logging toolincorporating the present invention;

FIG. 3 shows a detailed view of a part of the shuttle shown in FIG. 2;

FIGS. 4a-d show the positions of the parts of the actuating mechanism ofthe shuttle of FIG. 3 during various stages of deployment; and

FIG. 5 shows a partial view of another embodiment of the mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention finds particular application in multi-shuttleseismic logging tools. Such tools are used in VSP surveys and comprise anumber of identical or similar shuttles connected in end-to-end fashionby cable. A single shuttle is shown in FIG. 2 which comprises a toolbody 100, an anchoring mechanism 110 including an anchoring arm 120 anda sensor package 130. In use, a number of these shuttles, from 2 to 20,typically 4 to 8, are connected together and logged through the borehole140.

FIG. 3 shows a detailed view of the anchoring mechanism 110. Themechanism includes a permanent magnet (or electromagnet) brake 212,motor 214 and reducer arrangement 216 housed in the shuttle body 210.The output drive from the reducer 216 connects through a joint 218 andbearing 220 to a ball screw 222. The ball screw 222 drives a nut 224.The end of the screw 222 projects into the hollow end of a push rod 226and the end of the nut 224 engages the outer surface of the push rod 226through a clutch mechanism 228 which is described in more detail below.The end of the push rod 226 is connected to a link 230 through which itdrives the anchoring arm of the shuttle (120 in FIG. 2). The inner endof the push rod 226 is formed into a base section 232 which fits insidethe nut 224. The base section 232 also has extensions outside the nut224 to provide a connection to a potentiometer (or a linear variabledifferential transformer “LVDT”) 234 which acts as position sensor forthe push rod 226 and so can be used for a calliper measurement in theborehole using the anchoring arm. A compression spring 236 is locatedaround the motor/ball screw mechanism inside the shuttle body and actson the base section 232 so as to normally urge the push rod 226 andhence the arm, outwards. The extension of the push rod 226 under by thespring 236 is limited by the position of the nut 224 on the screw 222such that operating the motor 214 to move the nut 224 causes the pushrod 226 to move out due to the spring 236 or be pulled in by the actionof the nut 224.

Extension of the push rod 226 by the spring 236 is limited by either thearm contacting the borehole wall (FIG. 4c) or by the base section 232reaching the stops 238 positioned in the body (fully extended) (FIG.4b). Once the arm contacts the borehole wall, the nut 224 moves over thepush rod 226 to activate the clutch 228 such that the screw 222 and nut224 drives the push rod 226 directly and forces it against the boreholewall to anchor the shuttle (FIG. 4c).

To release the arm, the motor is reversed and the screw 222 retracts thenut 224, releasing the clutch 228. The arm is then only held against theborehole wall by the spring 236 and so can move in or out as the shuttleis moved to a different position in the well. It is not necessary toretract the arm completely. If it is desired to retract the armcompletely, the reverse motor drive is continued and the nut 224 isretracted along the screw 222 until it contacts the base section 232 ofthe push rod 226 which it then pulls back against the action of thespring 236 to retract the push rod 226 and thus the anchor arm. When thearm is fully retracted, the motor stalls and this is detected to findthe fully retracted/closed position of the arm. The output from thepotentiometer 234 can also be used to detect the arm in its fullyretracted position.

The clutch mechanism 228 (shown in more detail in FIG. 4a) is formed bythe outer end of the nut 224 through which the push rod 226 projects,and a collar 240 located in the shuttle body 210 around the push rod 226by a spring 242. The outer end of the nut has a number of seats 244 eachhaving a ball bearing 246 located inside. A retaining ring 248 preventsthe balls 246 from falling out of the seats 244. A number of grooves 250are formed in the outer surface of the push rod 226. As the end of thenut moves over the push rod 226 after it has contacted the wall of theborehole, the balls 246 are free to move in and out of the grooves 250without inhibiting movement of the nut 224, until the outer end of thenut 224 contacts the collar 240 (FIG. 4c). At this point, once the balls246 drop into the next groove 250, the collar is allowed to move overthe seats and prevent the balls 246 from moving out of the groove 250.Further motion of the nut 224 is transmitted to the push rod 226 by theballs 246 engaged in the groove 250 to provide the anchoring force forthe arm (FIG. 4d). Reversing the motor drive retracts the nut 224 fromthe collar 240 so allowing the balls to move out of the groove 250 andpermit the push rod to move back against the spring 236. The motion ofthe nut required to activate the clutch between first contacting thecollar 240 and driving or releasing the push rod 226 is small, forexample in the order of 3 mm. Thus the time to lock and unlock the armis small and has less impact on the time taken to move the shuttlebetween measurement locations.

In this arrangement, all of the drive mechanism and springs are locatedwithin the shuttle body with only simple mechanical linkages exposed.This is to be contrasted with the prior art mechanism which has the leafspring outside the tool. Also, eliminating the clutch and engagementmechanism between the motor and the screw and implementing the clutchbetween the nut and the push rod in the manner described above allows ashorter overall length.

An alternative embodiment is shown in FIG. 5 which has parts omitted forclarity. In this case, the potentiometer or LVDT 234 lies alongside theball screw 222. A position switch 252 is located alongside the push rod226 and clutch 228 to detect whether or not the clutch is engaged. Thisinformation is used in operation of the mechanism to actuate the tool.

Industrial Applicability

The present invention finds application in the field of borehole loggingtools, particularly seismic multi-shuttle logging tools which can beused to evaluate the formations surrounding boreholes such as aredrilled for the extraction of hydrocarbons or geothermal energy.

What is claimed is:
 1. A borehole tool comprising a tool body having atleast one sensor package and an anchoring mechanism, the anchoringmechanism comprising: a) a drive mechanism including a motor, a driveshaft and a clutch mechanism; b) an anchoring arm moveable between firstand second positions relative to the tool body; and c) a push rodextending through the clutch mechanism connecting the anchoring arm tothe drive mechanism, the push rod engaging a spring which acts to biasthe arm into the first position, and driveably connecting the drivemechanism through the clutch such that the arm can be moved between thefirst and second positions.
 2. A tool as claimed in claim 1, wherein theclutch mechanism comprises a collar having a number of balls whichengage grooves in the push rod to allow the drive mechanism to move thearm.
 3. A tool as claimed in claim 2, wherein the clutch mechanismincludes a spring-loaded retaining ring which causes the balls to beheld in a driving position in the grooves when engaged by the collar. 4.A tool as claimed in claim 1, wherein the drive shaft comprises a drivescrew which acts on the clutch mechanism by means of a nut to transmitdrive to the push rod.
 5. A tool as claimed in claim 4, wherein the nutis provided with surfaces which engage extensions of the push rod toallow the drive mechanism to act on the push rod to move the arm to thesecond position.
 6. A tool as claimed in claim 1, wherein the springcomprises a coil spring surrounding at least part of the drivemechanism.
 7. A tool as claimed in claim 1, wherein the drive mechanism,push rod and spring are all located within the tool body.
 8. A tool asclaimed in claim 1, wherein the first position of the arm has the armextending away from the tool body so as to engage a wall of a boreholein which the tool is positioned, and the second position of the arm hasthe arm lying close to the tool body.
 9. A tool as claimed in claim 8,wherein the drive mechanism is used to control the movement of the armunder the influence of the spring between the first and secondpositions, and can also act to further urge the arm to the firstposition so as to apply force to the borehole wall.
 10. A tool asclaimed in claim 9, wherein the spring and the drive mechanism operateso as to cause the arm to engage the borehole wall and force the toolbody against the opposite side of the borehole wall, the drive mechanismserving to provide extra force to anchor the tool body against theborehole wall while measurements are made using the sensor package. 11.A tool as claimed in claim 9, wherein the drive mechanism can bereversed to disengage the clutch mechanism and remove the extra forcefrom the arm such that it only engages the borehole wall under theinfluence of the spring.
 12. A tool as claimed in claim 10, wherein thedrive mechanism can be reversed to disengage the clutch mechanism andremove the extra force from the arm such that it only engages theborehole wall under the influence of the spring.
 13. A tool as claimedin claim 1, further comprising an arm position sensor.
 14. A tool asclaimed in claim 13, wherein the sensor is a potentiometer.
 15. A toolas claimed in claim 1, wherein the arm is mounted on a pivot on the toolbody, the push rod engaging an extension of the arm through a link. 16.A tool as claimed in claim 1, further comprising a position sensor forindicating the state of the clutch mechanism.